One of China's largest internet companies has had two of its licences revoked by the Government because of online pornography.

Chinese state media announced the blocking of some of the output of Sina.com, which runs the Weibo social media site, among others.

It followed the discovery of 20 articles and four videos containing pornographic and lewd content, the official Xinhua news agency said.

Sina apologised for "the suspected problem" and said on its website that it felt "sorry and ashamed" for lax monitoring.

It added that it had moved quickly to rectify the problem.

Xinhua said some people are being investigated by police as a result.

Xinhua quoted a government statement, saying: "Some of these articles were as long as 500-plus chapters and clocked millions of clicks ... imperilling social morals and seriously harming minors' physical and mental health."

It said the state broadcasting authority had therefore decided to revoke Sina's licences on internet publishing and online audiovisual broadcasting and impose "a large number of fines".

It is thought the action may hamper Sina's ability to operate in China but it is not known which sites or content will be hit.

Weibo has a 55% share of all microblogging in China, according to the company, with more than 280 million users and millions of posts a day. It is generally regarded as China's equivalent to Twitter.

China's Communist authorities heavily police the internet for content deemed obscene or politically subversive. Twitter, Facebook, and other Western social media sites are blocked.

In the government's latest campaign against online pornography, the State Internet Information Office has shut down 110 websites and some 3,300 accounts on China-based social networking sites as of the past weekend, according to Xinhua.

The loss of its licences comes barely a week after Weibo launched on the Nasdaq stock exchange in the US.